System for filtering ultrasonic noise within a fluid flow system

ABSTRACT

A method is employed to attenuate ultrasonic noise propagating in a flow stream of a fluid flow system. In particular, the method attenuates the noise propagating between a noise source and a reference point in the flow stream (wherein the reference point and the noise source are positioned in the flow stream in direct acoustic line of sight relation). The method includes positioning an absorbent element in the flow stream between the noise source and the reference point. Then, the ultrasonic noise is directed past vicinity of the absorbent element such that indirect ultrasonic noise is absorbed by the absorbent element. Preferably, the method also includes deflecting the ultrasonic noise to convert direct noise to indirect noise prior to directing the ultrasonic noise past the vicinity of the absorbent material in the flow stream. Such a method may be employed to attenuate ultrasonic noise by up to about 20 dB to 45 dB.

The present invention claims the benefit of the filing date of U.S.Provisional Application Ser. No. 60/411,572 filed Sep. 18, 2002 (nowpending). The above Provisional Application is hereby incorporated byreference for all purposes and made a part of the present disclosure.

BACKGROUND OF THE INVENTION

The present invention relates generally to a system, apparatus andmethod for filtering acoustic noise within a fluid flow system. Moreparticularly, the invention relates to the mitigation or attenuation ofultrasonic noise, and the incorporation of such an apparatus within afluid flow system that includes a noise source and an ultrasonic device.Further, the invention relates to the elements or components of such anapparatus, particularly directed to attenuating direct and/or indirectnoise within a fluid flow environment.

Sound or noise is a longitudinal mechanical wave motion in an elasticmedium and is classified according to its frequency—infrasonic, audible,and ultrasonic. The infrasonic classification refers to frequenciesbelow the detection level of the human ear (less than 20 Hz). Theaudible classification refers to frequency that can be detected by thehuman ear (from 20–20,000 Hz). The ultrasonic classification refers tofrequencies above the detection level of the human ear (above 20,000Hz). Sensory effects of sounds denoted by a physiologist as loudness,pitch, and quality are correlated with the measurable parameters ofsound denoted by physicists as intensity, frequency and wave shape.

The intensity of a sound wave is the amount of wave energy transmittedper unit time per unit area normal to the direction of soundpropagation. That is, the intensity of sound is the power transmittedper unit area. In the audible classification of noise, the significantintensities for a human species are:

Noise Intensity (W/M₂) Level (dB) Hearing Threshold 1 E-12 0 Whisper 1E-10 20 Conversation 1 E-06 65 Street Traffic I E-05 75 Train in aTunnel 1 E-02 100 Pain Threshold 1 E-00 120

Acoustics is a systematic investigation of the nature, origin, andpropagation of sound. Acoustic noise generation in a closed conduit canoccur from many sources, including protruding gaskets, misaligned pipeflanges, headers, line size changes, valves, etc. The flowing velocityin the pipe is a major factor in the character of the acoustic noise.When pipe velocity is below 50 fps, one would expect noise from only acontrol valve, which is designed to manipulate the flow. When the pipevelocity is greater than 50 fps, noise generation can be initiated by amultitude of the aforementioned sources.

Sound waves are pressure pulses propagate in accordance with acousticplane wave theory. Sound propagates as a pressure wave in gas flowsystem, i.e., pipe system or other fluid conduit, at the velocity ofsound of the fluid. Such a propagating pressure wave will be reflectedand absorbed at impedance discontinuities forming standing wave patternsor acoustic resonances. These resonances typically amplify pulsation bya factor of 10 to 100.

Noise travelling along the longitudinal direction, i.e., in parallelwith the longitudinal centerline of the conduit, may be referred to asdirect noise. Noise travelling in a direction that is not parallel to,or not oblique with respect to, the longitudinal centerline may bereferred to as indirect noise. Direct noise may become indirect noiseupon encountering a bend, obstruction, or certain discontinuities in theflow medium, that forces the pressure wave to reflect, refract orotherwise deviate from the direct or longitudinal direction. Indirectnoise may, therefore, propagate through a extensive run of conduit bybouncing or reflecting off the walls of the conduit.

BRIEF SUMMARY OF THE INVENTION

In one aspect of the present invention, a fluid flow system is providedthat includes a fluid flow conduit, a noise source disposed in the fluidflow conduit such that ultrasonic noise generated by the noise sourcepropagates therein, and an ultrasonic noise filter apparatus alsodisposed in the fluid flow conduit. The ultrasonic noise filterapparatus includes a first and a second noise filter. The first noisefilter has an absorbent element that is constructed to attenuateultrasonic noise propagating from the noise source in the direction ofthe first and second noise filters. The second noise filter isadvantageously disposed in the fluid flow conduit between the firstnoise filter and the noise source and includes a deflector elementpositioned to deflect ultrasonic noise propagating from the noise sourcebefore the ultrasonic noise passes to the first noise filter.

In this inventive fluid flow system, the deflector element is preferablyacoustically positioned so as to provide the sole direct line of sightacoustic obstruction between the noise source and the first noisefilter. In other words, the noise source and the first noise filterwould be disposed in direct line of sight acoustic relation if not forthe presence of the second noise filter. More preferably, the fluid flowsystem includes an ultrasonic device (e.g. an ultrasonic flow meter)that is operable at ultrasonic frequencies. The ultrasonic device ispositioned in the fluid flow conduit such that the first and secondnoise filters are intermediate the ultrasonic device and the noisesource. Further, the second noise filter preferably provides the soledirect line of sight obstruction between the ultrasonic device and thenoise source.

In another aspect of the invention, a method is provided for attenuatingultrasonic acoustic noise in a fluid flow system between a noise sourceand a reference point. The reference point and the noise source aredisposed in fluid communication such that absent any flow obstructiontherebetween, the noise source and the reference point (e.g., anultrasonic flow meter) would be positioned in direct line of sightacoustic relation and such that noise generated by the noise sourcepropagates between the noise source and the reference point through afluid flow path defined therethrough. The inventive method includes thesteps of eliminating a direct acoustic line of sight between the noisesource and the reference point and positioning an absorbent material inthe flow path and in generally parallel relation therewith. During flowconditions, the absorbent material is utilized to absorb indirect noisepropagating through the flow path and converting the absorbed indirectnoise to vibration. Preferably, the step of eliminating the direct lineof sight is performed acoustically upstream of the point where the stepof absorbing is performed.

In another aspect of the invention, an ultrasonic acoustic noise filteris provided for incorporation into a fluid flow conduit and forattenuating ultrasonic noise propagating in the fluid flow conduit. Thisinventive noise filter includes a flow entrance, a flow exit, aplurality of channels extending between the flow entrance and the flowexit, and an absorbent element supported within one or more of thechannels. Each of the channels defines a flow path between the entranceand the exit. Further, the absorbent element includes an absorbentmaterial disposed in generally parallel relation with the flow path andconfigured to absorb indirect ultrasonic noise propagating in the flowpath.

In yet another aspect of the invention, the ultrasonic noise filterincludes a flow entrance and a flow exit that define a flow paththerebetween and has a longitudinal centerline. The noise filter furtherincludes an absorbent element disposed in the flow path. This absorbentelement has lateral sections of absorbent material which are configuredto absorb indirect noise propagating in the flow path. The lateralsections are disposed generally parallel with the flow path and areformed by spirally wound layers of the absorbent material. The absorbentmaterial is preferably a fibrous, polyester material.

In yet another aspect of the invention, a method is employed toattenuate ultrasonic noise propagating in a flow stream of a fluid flowsystem. In particular, the method attenuates the noise propagatingbetween a noise source and a reference point in the flow stream (whereinthe reference point and the noise source are positioned in the flowstream in direct acoustic line of sight relation). The method includespositioning an absorbent element in the flow stream between the noisesource and the reference point. Then, the ultrasonic noise is directedpast vicinity of the absorbent element such that indirect ultrasonicnoise is absorbed by the absorbent element. Preferably, the method alsoincludes deflecting the ultrasonic noise to convert direct noise toindirect noise prior to directing the ultrasonic noise past the vicinityof the absorbent material in the flow stream. In the above manner, amethod according to the invention may be employed to attenuateultrasonic noise by up to about 20 dB to 45 dB.

In yet another aspect of the invention, a fluid flow system is providedincluding an ultrasonic device, a noise source and an ultrasonicacoustic noise filter. The ultrasonic device is a device such as anultrasonic flow meter that is operational at ultrasonic frequencies. Thenoise source, which may be any one of a number of ultrasonic noisegenerators including control valves and flow regulators, is disposed inthe fluid flow conduit and in fluid communication with the ultrasonicdevice and the noise filter. The ultrasonic acoustic noise filter isalso disposed in the fluid flow conduit, between the ultrasonic deviceand the noise source, and in fluid communication with both components soas to define a fluid flow stream therebetween. Further, the noise filterincludes an absorbent element for attenuating ultrasonic noisepropagating from the noise source in the direction of the ultrasonicdevice.

In a preferred embodiment, the absorbent element is positioned ingeneral parallel relation with the flow stream. Thus, the absorbentelement is particularly adapted to absorbing indirect ultrasonic noiseand/or converting noise energy into kinetic energy (i.e., vibrationswithin an absorbent material of the absorbent element). A preferredabsorbent element has or consists of an absorbent material constructedof multiple spirally-wound, overlapping layers of fibrous material(e.g., polyester, polypropylene, or combinations thereof), therebycreating protrusions into the flow stream (for effecting turbulence).The fibrous network or components of the absorbent material are alsoparticularly adapted to absorbing noise energy and effecting vibrationsas a result thereof.

Thus, in one method of attenuating ultrasonic noise in a fluid flowsystem according to the invention, absorbent material is positioned inthe flow stream between the noise source (e.g., a control valve) and areference point (for purposes of evaluating the degree of attenuation)(e.g., an ultrasonic flow meter). Preferably, the absorbent material ispositioned in generally parallel relation with the flow stream and thus,generally obliquely with the propagation direction of indirect noise.The ultrasonic noise is then directed past the vicinity of the absorbentmaterial, such that at least some of the indirect noise energy in theultrasonic noise is absorbed by conversion into kinetic energy (e.g.,vibration within the absorbent material).

In yet another aspect of the inventive method, ultrasonic noisepropagating from the noise source is first manipulated, e.g., deflected,to transform some of the direct noise into indirect noise, prior toencountering the absorbent material. For example, the ultrasonic noisemay be directed through a flow-through device to eliminate a directacoustic line of sight relation between the noise source and a referencepoint downstream of the noise source. The ultrasonic noise is thendirected downstream in the vicinity of the absorbent material, such thatindirect noise is absorbed by the absorbent material. In this manner,the inventive method may be employed to eliminate between about 20 dB toabout 50 dB of ultrasonic acoustic noise.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a prior art fluid flow system;

FIG. 2 is a schematic of a fluid flow system according to the presentinvention;

FIGS. 3 and 3A–3D are various views of en exemplary ultrasonic noisefilter for deflecting and thereby attenuating ultrasonic noise, andparticularly suited for use with a system, apparatus, and/or methodaccording to the present invention;

FIG. 3E are performance results of the noise filter shown in FIGS. 3 and3A–3D;

FIGS. 4 and 4A–4H are various views of another set of exemplaryultrasonic acoustic noise filters according to the invention;

FIGS. 5A–5C are various simplified illustrations of a preferred flowchannel within a noise filter according to the invention, and includingan absorbent material or absorbent element according to the invention;

FIGS. 6A–6F are various simplified schematics of fluid flow systems inaccordance with or embodying various aspects of the present invention;and

FIGS. 7A–7B are performance results of noise filters for use with thepresent inventive method.

DETAILED DESCRIPTION OF THE INVENTION

For purposes of illustration, the following description focuses on anapplication wherein an acoustic filter according to the invention isincorporated in the fluid flow system including an ultrasonic devicesuch as a multi-path ultrasonic meter, and a noise source, such as acontrol valve. Again, for purposes of illustration, the followingdescription focuses on the problems and disadvantages presented by priorart systems including such an ultrasonic device and noise source, andpreferred embodiments of the inventive system, apparatus and methodparticularly suited to address these problems and disadvantages. FIG. 1depicts such a prior art fluid flow system 108 and is briefly describedbelow.

FIGS. 2–7 depict ultrasonic noise filters and fluid flow systemsincorporating such filters, or illustrate a method or performanceassociated with those noise filters, each of which embody variousaspects of the invention. Upon review of the Detailed Description andthe accompanying drawings provided herein, it will become apparent toone of ordinary skill in the art, however, that the present invention isalso applicable to the other applications and to addressing other fluidflow and noise problems. For example, it will be apparent that theultrasonic acoustic filter described herein may be installed in otherfluid flow systems, whether gas or liquid flow, and in combination withother fluid flow elements. It will also become apparent that variouselements of the ultrasonic acoustic filter provided herein (e.g., theconstruction of an ultrasonic noise absorbent element) may beincorporated with other acoustic noise managing devices and methods, notnecessarily including all of the preferred components described herein.Moreover, it will become apparent that the invention encompassesvariations of the preferred acoustic filters and preferred fluid flowsystems described herein, as well as various methodologies utilizingsome of these components.

The U.S. Occupational Safety and Health Act of 1970 (OSHA) establishedmaximum permissible noise levels for all industries whose businessaffects interstate commerce. These permissible levels apply, of course,to industries concerned with fluid flow systems. In one method ofaddressing audible noise levels, certain processes and operators oftenconvert the noise to the ultrasonic range, thereby generating yet asecondary source of ultrasonic noise.

As suggested above, control valve noise becomes a particular concern athigher pipe velocities. Control valve noise is a particular problemencountered with the installation and operation of ultrasonic meters(and other ultrasonic devices). In particular, control valve noise is aproblem that has to be addressed when installing multi-path ultrasonicmeters for natural gas applications. Other particularly problematicnoise sources in these flow environments are flow regulators and pipinginduced disturbances.

Referring to the schematic of FIG. 1, in a typical ultrasonic meterapplication, a control valve 110 or other noise source will be placedupstream or downstream of an ultrasonic meter 112. Current practicesdictate that the control valve 110 should be placed downstream of themeter 112 to ensure that the acoustic noise generated by the valve 110does not “scramble” the acoustic signal of the ultrasonic meter. Varioustechniques are commonly employed to minimize the impact of theultrasonic noise generated by the control valve 110 (none of whichincludes the use of an ultrasonic acoustic filter). In the particularcase of multi-path ultrasonic metering station, it is a typicalrecommendation that either the control valve or regulator be locateddownstream of the meter 112. The noise generated from typical controlvalves normally covers a wide frequency range, part of which willinclude the operating range of the ultrasonic meter itself, e.g.,100–200 KHz. It is a particular challenge when the meter is operatingand encounters noise levels in excess of its normal operating range. Ina typical frequency response curve for a control valve, a peak frequencyemitted will be approximately 60 kHz. However, it is important toillustrate that even at the higher frequencies, 100–200 KHz, it can beseen that the noise level may be in excess of 130 dB. The ultrasonicmeter may operate effectively up to a noise level of 90 dB, however,above that level, the noise may be too extreme for the meter to overcome(e.g., using its traditional signal processing and gain controlregimes). At this point, it becomes clear that the meter will startlosing pulses during the transmission and reception cycle and becomeinoperable or marginally functional depending upon the noise levelsbeing experienced.

The level of noise generated is dependent on: flow rate; pressure dropacross the valve or restriction; and the type of valve or restriction.In one aspect of the invention, an ultrasonic acoustic filter isprovided which accommodates the extreme noise reduction scenario of highvelocity with high pressure drop, through an ultrasonically noisyrestriction (such as a valve or pipe restriction).

Currently, manufacturers and operators employ different noise mitigationtechniques in the meter itself ranging from increasing the amplitude ofthe pulse transmitted sometimes coupled with complex digital signalprocessing techniques. However, while the amplitude of the noise remainsabove that which the meter can effectively operate, it will be difficultto establish a working environment for such a meter. Thus, mostmanufacturers now consult with the operator to ensure that the meter hasa better chance at successful operation by establishing installationcriteria. For example, the manufacturer may recommend deployment ofhigher frequency transducers. The operation of higher frequencytransducers does not guarantee, however, elimination of the noiseproblem entirely. From the frequency response curve, it can be seen thatthe noise levels at the higher frequencies, while being less than thelower frequencies, are not significantly reduced.

Secondly, the manufacturer may recommend the installation of multipleblind tees, elbows, or crosses between the source of the noise and themeter. The installation of FIG. 1, which includes blind tees (orcrosses) 114, adopts this recommendation. With regard to the use ofmultiple “blind” or dead ended tees and elbows, this creates a number ofchallenges for the piping designer. For example, this adds to thecomplexity, extent, and efficiency of the piping system. Moreover, sucha number of obstruction in the piping system presents potential erosionchallenges, especially at the higher velocities. Such a complex pipingconfiguration also provides an increased number of potential leakagesites and potential maintenance problems. In any event, the blind teearrangement 114 of FIG. 1 may be expected to attenuate ultrasonic noisegenerated by the control valve by up to 8 dB.

In one aspect of the invention, a system and apparatus is provided forfiltering ultrasonic noise in a fluid flow system, utilizing a minimumnumber of piping disturbances and a simpler configuration. In yetanother aspect of the invention, a system for filtering ultrasonic noiseis provided wherein the noise source, noise filtering apparatus orsystem, and ultrasonic device are provided along a relatively straightpiping run, wherein the ultrasonic device and the noise source wouldotherwise be acoustically positioned along a direct line of sight (orsimply, line of sight (LOS)). When there is a direct acoustic line ofsight relation between the noise source and the ultrasonic device,ultrasonic noise generated by the noise source could otherwise propagatein a generally direct fashion to the ultrasonic device withoutreflection or obstruction.

Referring to FIG. 2, a preferred fluid flow system 208 according to theinvention includes an noise source such as a control valve 210, anultrasonic device such a flowmeter 212, a first noise filtering deviceor noise filter 214, and, optionally, a second noise filtering device ornoise filter 216. The first and second filtering devices 214,216 may beregarded also as one noise filtering apparatus or system.

As shown in the Figure, the control valve 210 and the meter 212 aredisposed in fluid communication in a substantially straight piping runand are acoustically positioned such that, absent any obstructions inthe flow stream, would (otherwise) be in direct line of sight relation.In such a system 208, the ultrasonic noise generated by control valve210 has a substantial direct noise component or focus. Thus, in oneaspect of the present inventive method, the ultrasonic noise propagatingtherefrom is first deflected by a deflector element such as second noisefilter 216. In this manner, the line of sight relation between thecontrol valve 210 and the meter 212 is eliminated. This also means thatmuch of the direct noise generated by the control valve 210 istransformed into indirect noise by way of deflection (or by travelingthrough turbulent flow regions).

Although, attenuation of the ultrasonic noise does occur through use ofthe second noise filter 216, the preferred method employs a second phaseor operation to further attenuate the ultrasonic noise. Locateddownstream of the second noise filter 216, the first noise filter 214receives much of the indirect noise exiting the second noise filter 216,which at this stage may be propagating off the walls of the pipeconduit, at a rate depending partially on the pipe configuration andspacing between the filters 214, 216. In any event, according to thepreferred method, the first noise filter 214 operates to absorb much ofthe indirect noise received therein, e.g., by converting ultrasonicnoise energy to vibration within or of an absorbent material, therebyfurthering attenuating the ultrasonic noise to a significant degree.

In the manner described above, attenuation of the ultrasonic noise canbe attained at levels up to about 40 to 50 dB. It should be noted,however, that some of the attenuation can be attributed to other modesother than the deflecting and absorbing operations described. As willbecome apparent with the more detailed descriptions of the systems andapparatus provided below, the noise filters 214,216 (and othercomponents in the fluid flow system) also have the capacity to reflect,deflect, absorb, or otherwise attenuate ultrasonic noise in other ways.

The illustrations of FIGS. 3 and 3 a–3 c depict an exemplary ultrasonicacoustic noise filter 310 for use with the inventive system and method.In particular, the acoustic noise filter 310 is designed to convertsystematic motion of the fluid into uncoordinated random motions.Specifically, as the fluid passes through the acoustic noise filter 310,the noise filter 316 acts to isolate the piping system, by eliminatingthe line of sight relation between the noise source and the referencepoint, e.g., between the control valve and the meter. In this respect,the noise filter 310 is a suitable specific embodiment of the secondnoise filter 216 described above with respect to FIG. 2.

As shown in the perspective view of FIG. 3, the acoustic noise filter310 includes a plurality of flow through ports 316 at an upstream orentrance face 312. The ports 316 are spaced about the face 312 in acoordinated predetermined manner and so as to provide a suitableporosity value for the filter 310. In one aspect of the invention, theports 316 is split into a first flow channel 316 a and a second flowchannel 316 b by way of a helix 318. Each of the flow channels 316 a and316 b extend through the length of the acoustic noise filter 310 toprovide a flow stream thereacross. The helix 318 is inserted in the port316, however, to split and deviate the flow in a rotative manner. Moreimportantly, the helix 318 provides an obstruction in the longitudinaldirection of the port 316, thereby eliminating the direct acoustic lineof sight relation between the entrance and the exit, and more broadly,between the noise source and the reference point, e.g., the controlvalve and meter. In this manner, attenuation of ultrasonic noise may beeffected by approximately 8 dB.

FIG. 3 c is plain view illustration of the entrance face 312 of thenoise filter 310. In particular, FIG. 3 c charts the flow orientation ofeach port 316 (and the flow channels 316 a, 316 b provided therein). Asshown in the illustration, each of the pair of flow channels 316 a, 316b is either rotated (by way of the helix 318) in a clockwise or right(“R”) or in the counter-clockwise or left (“L”) direction. Further, eachof the ports 316 is positioned such that each right rotating pairs offlow channels 316 a, 316 b is adjacent a left rotating pair of flowchannels 316 a, 316 b. In this way, at the downstream side of the noisefilter 310 c, individual flows exit in the clockwise orcounter-clockwise direction. Further yet, each counter-clockwiseindividual flow stream is positioned adjacent an oppositely rotating orclockwise rotating flow stream. In this way, a field of turbulence isprovided immediately downstream of the noise filter 310. It has beenfound that the provision of such a field of turbulence functions tofurther deflect (and attenuate) ultrasonic noise propagating through theflow stream.

Referring to FIG. 3 d, the helix 318 c can be made from most metallic orother rigid structure, preferably sealably welded within the port 316.In preferred embodiments, a 10″ flow I.D. noise filter 316 may beconfigured so as to have a flow length of about 2–2½″. In the case ofsuch a 10″ noise filter 310, the ports 316 preferably have a 1.5″diameter.

FIG. 3 e provides a summary of field tests or trials for an acousticnoise filter such as noise filter 310.

FIG. 4 illustrates an exemplary ultrasonic acoustic noise filteraccording to the invention. More specifically, the noise filter 410depicted in these figures are particularly suited for absorbing indirectnoise propagating therethrough, in the order of about 40 to 50 dB. Asfurther described below, the noise filter 410 provides an absorbentelement having absorbent material thereon which converts indirect noisepropagation into vibration (and, also thereby converting the indirectnoise energy into small amounts of thermal energy). In yet anotheraspect of the invention, the noise filter 410 may be incorporated into afluid flow system wherein the noise source and a reference point, e.g.,a control valve and an ultrasonic flow meter, are acousticallypositioned in direct line of sight relation. Further, the noise filter410 is particularly suited for incorporation into the flow system 208 ofFIG. 2 as the first noise filter 214.

Now turning to the simplified illustrations in FIG. 4, an exemplaryultrasonic acoustic noise filter 410 is shown therein, particularlysuited for absorbing indirect noise so as to attenuate the ultrasonicnoise by or up to 40–50 dB (gross noise absorption). FIG. 4 and FIG. 4a–4 h provide details for a noise filter 410 designed for installationin a 10″ piping flow system. The noise filter 410 includes an upstreamside 412, a downstream side 414, and a longitudinal structural centerline XX. On the upstream side 412, the profile of the noise filter 410is defined by a mounting ring 426 supporting a front webbing plate 416.The front webbing plate 416 provides a plurality of flow channels 418,each of which has a flow through, see through flow configuration. Inthis particular embodiment, the webbing plate 416 defines a group of sixoutside channels 418 surrounding a central or inside channel 460.Further yet, the configuration of outside channels 418 and insidechannel 450 defines additional flow channels 434 positionedtherebetween.

With reference also to FIGS. 4 a–4 h the noise filter 410 also includesa canister or housing 430 that mates with the webbing plates 416, and adownstream webbing plate 444. As best illustrated in the cut out of FIG.4 c, these components house or maintain a plurality or bundle ofabsorbent elements 420. As will be discussed further below, theabsorbent element 420 is made up of longitudinally extending absorbentmaterial which provides an absorbent surface for indirect noise. Theabsorbent element 420 is further maintained in place by way of threadrods 432 that extend between the webbing plate 416 and the downstreamwebbing plate 444. The thread rods 432 further support the components ofthe noise filter 410, but specifically compressibly supports theabsorbent element and material 420. It has been shown that the additionof the thread rod 432 provides advantageous structural integrity toabsorbent element 420. In particular, such structural support enhancesthe rigidity and the ability of the absorbent element 420 to vibrate inthe desired manner.

As illustrated by the Figures, each of the flow channels 418, 460, andeven flow channel 434, provides a substantially straight through, seethrough, individual flow path. Each of channel 422 is defined by aninside surface provided by the absorbent material 420, as well as anexposed surface (i.e., free of absorbent material 420). In relation tothe individual flow paths through the channels 422, 434, 450, theabsorbent material is positioned in parallel relation to thesubstantially straight through flow path and each of the individualchannels 422, 450, and 434. In other words, absorbent material will beadvantageously positioned obliquely with respect to the indirect noise,but in parallel with direct noise.

Referring specifically to FIG. 4 b, each of the outside channels 422 maybe defined by a maximum gap YY between the exposed surface 450 and theabsorbent surface defined by the absorbent material 420. In thepreferred design configurations, applicants have found that optimaldesigns may be partially dictated by maintaining the maximum gap YYconstant between noise filters in the 4″ to 12″ pipe diameters. As thepipe diameter varies, the number of outside channels are required tovary also (as the inside circumference of noise filter 410 also varies).This variance is further accommodated by providing and varying the sizeof inside channel 420. This is best illustrated in FIG. 4, whereinvarious webbing plate configurations are denoted by the pipe diameter.For example, for a 4″ configuration, 3 or 4 outside channels are used incombination with a single inside channel. For a 16″ pipe configuration,6 outside channels are used in combination with an inside channel aswell as six intermediate channels.

Referring back to FIGS. 4 a and 4 b, it is evident that the intermediatechannels 434 are a product of the orientation of the outside channels418 and inside channel 460. That is, the inside surface of theintermediate channels 434 are the backsides of the absorbent element420, which define the outside channels 418 and inside channel 460. Thus,in one aspect of the invention, a unique configuration of flow throughchannels and absorbed materials is provided so as to optimize thesurface area of the absorbent material as well as maintaining structuralintegrity and efficient use of materials. Moreover, in an aspect of theinvention, the optimization of the design of the noise filter 410becomes a function of or is motivated in varying degrees by the totalsurface area of absorbent material, the size and number of the flowchannels particularly the inside and outside channels (e.g., maintaininga maximum gap YY), porosity, the length of the flow channels, and thepipe size. These parameters are, of course, related, e.g., totalabsorbent surface is a function the flow channels sizes andconfigurations, and the length of the flow channel.

Porosity is also inter-related with these parameters, e.g., increasingor decreasing the flow channel sizes affects the porosity of the noisefilter 410 (because porosity is the ratio of the unrestricted torestricted area to flow). It is common to maximize the unrestricted flowfor flow purposes, however, this is weighed against the structuralrequirements of the device. For the various embodiments of the noisefilter 410 as depicted in FIG. 4, the porosity is preferably about40–70%, the porosity and more preferably in the range of about 44–64%

As alluded to above, optimization of the noise filter 410 design issignificantly governed or motivated by parameters relating to theabsorbent material 420. In addition to surface area, the thickness ofthe absorbent material 420 and the maximum gap YY is also of importance.

In any case, FIGS. 4 and 4 a–4 h are provided to show preferredconfigurations, dimensions, material selections, and other designconsiderations and parameters for a noise filter 410 according to thepresent invention. Details of the preferred and/or optimal designs(including dimensions and surface areas) may be derived from these “toscale” construction drawings. For this purpose, a set of drawingsapplicable to a 12″ embodiment of the noise filter 410 is also provided.

The simplified diagrams of FIG. 5 illustrate in some detail theconstruction of the noise filter 410, particularly in and around theflow pattern. More importantly, diagrams illustrate the behavior offluid flow and acoustic wave motion within and through the flow channel.In these drawings, reference ZZ is used to denote propagation of highfrequency sound wave (i.e., ultrasonic noise). It is important to notethe direction (i.e., direct and indirect; reflective, direct) as well asintensity of strength of the sound wave illustrated. Reference WW isused to denote fluid flow, which, in the exemplary case, is gas flow.Finally, reference VV is used to denote a fluid area or field ofturbulence.

FIG. 5A provides a longitudinal cut-out of one of the flow channels 418,specifically the portion defined by the wall surface of the absorbentmaterial 420 (as opposed to the exposed wall surface). FIG. 5B is a yetanother cut-out from the FIG. 5A, but in perspective view. FIG. 5C is adetail cross-sectional of a portion of FIG. 5A to illustrate (in bothsimplified and exaggerated terms), certain fluid and acoustic dynamicsas would occur in the operation of a method of attenuation according tothe present invention.

In yet another aspect of the invention, the absorbent element 420 (oracoustic element) of the noise filter 410 is provided with or consistsof an absorbent material 420 advantageously configured and positionedwithin the flow stream WW to absorb, and thereby, attenuate indirectnoise. The absorbent material 420 selected is both capable of absorbingindirect noise and is mechanically sound. In particular, the absorbentmaterial is adapted to converting ultrasonic noise energy into kineticenergy in the form of elicited vibrations in the absorbent material.Further, the selected material is able to withstand both water andhydrocarbon saturation.

In preferred embodiments of the invention, a hard, manmade, fibrousmaterial is used as the absorbent material. Moreover, the material isprovided in a cylindrical configuration, formed by a very large numberof the material layers 518 (see e.g., FIG. 5B). The material layers 518are preferably spirally or helically wound to form overlapping layers(e.g., 150 layers for 3″ to 5.5″ OD×12″ long tube)). More preferably,the absorbent material 420 includes several laterals sections 518 a ofpolyester and propylene media formed in a conical helix pattern. Eachlateral section consists of multiple helically or spirally wrappedlayers 518. Thermally bonded, the layers 518 are applied to conform andoverlap previously-applied layers, thereby forming the conical helixstructure.

One advantageous aspect of this configuration is the formation ofprotrusions or steps 522 at the transition points or areas betweenlateral sections. As discussed below, these steps 522 function to effectadditional regions or fields of turbulence VV within the flow channel420. As best shown in FIG. 5C, the absorbent material 420 provides arough, uneven surface due to the steps 522 as well as the fibrousmaterials or fibers 512, a significant portion of which protrude intothe flow stream WW. Applicants have discovered that such an absorbentsurface disposed in the flow path and in parallel relation therewith,enhances the absorption of ultrasonic noise.

The fibrous material or fibers 512 presents a cellular construction ornetwork that is particularly adapted to propagating and transferringvibration energy through the absorbent material. The fibers 512 functionas vibrating elements suspended from the rest of the absorbent material420 or base. The fibers 512 also contribute to the rough texture of theabsorbent surface, hereby also effecting some degree of turbulence VV.

One preferred absorbent material particularly suited for the embodimentsdescribed herein is a coreless and spirally wound filter element asdescribed in U.S. Pat. No. 5,827,430, hereby incorporated by referenceand made a part of this disclosure. The '430 patent also discusses asuitable construction of the absorbent material. It should be, noted,however, that the material taught in the '430 patent is designed andintended for a gas flow filtering operation (and not contemplated fornoise management or absorption). For this and other reasons, thediscovery of the advantageous application of such fibrous material inthe present ultrasonic noise attenuating application was very unexpectedand fortuitous.

As best shown in FIGS. 5B and 5C, the flow channel is also characterizedby a lip pr dam structure 510 at the entrance face. The lip or dam 510is created by providing an entrance radius that is less than the insidediameter or radius of the absorbent material 420. In other words, themaximum gap between the absorbent surface and an oppositely facingsurface is greater than the same gap with respect to the dam 510. Asshown in FIG. 5C, as fluid flow WW enters the flow channel 418, the dam510 effects a turbulence region VV immediately downstream thereof.Additional turbulence fields VV are also effected downstream along thelength of the flow channel 418, including radially inward of the steps522 and of the fibers 518 Such turbulence contributes to the deflecting,bending, or otherwise conversion of more direct noise to randomlydirected noise and thus indirect noise, which can be absorbed by theabsorbent material 420. The turbulence field VV generated, therefore,enhances the capacity of the noise filter 410 to attenuate ultrasonicnoise.

Thus, when indirect ultrasonic noise ZZ enters the flow channels 418 ofthe noise filter 418, much of the indirect noise component of theultrasonic noise ZZ make contact with the absorbent material 420. Someof the ultrasonic noise encounter the surface areas of the webbing plateand of the dam, and are reflected therefrom. More enter the flow channel418 and are further deviated from a direct path by turbulence fields VV.Much of the indirect noise ZZ hit the absorbent material 420, ispartially absorbed, then deflect back into the flow channel 418. Suchabsorption and deflection pattern of the ultrasonic noise ZZ continuesalong the length of the flow channel 418. In any event, a significantportion of the ultrasonic noise is absorbed by the absorbent material,by converting the kinetic energy of the noise into kinetic energy orvibration of the fibrous network of the absorbent material 420.

In another aspect of the invention, the mechanical integrity of theabsorbent materials or bundles of the absorbent material (see e.g. 420in FIGS. 4 b–4 c) is maintained and enhanced by addition of compressiblesupports. In a preferred embodiment, as illustrated in FIG. 4,compressible supports are provided in the form of longitudinallyextending tie rods 432. Additional support is provided by the mountingring, webbing plates, and housing, but the total effect is amechanically supported absorbent structure also having the desiredrigidity and resiliency particularly suited to absorbing ultrasonicnoise energy.

In a preferred deployment of acoustic filters according to theinvention, and incorporation into a fluid flow system, the inventiveacoustic noise filter as illustrated in FIG. 4, is provided in a fluidflow system including a noise source and a meter. For example, in afluid flow system including an ultrasonic meter and a control valve, theacoustic noise filter 410 is provided in the fluid flow system and influid communication with the ultrasonic meter and control valve.

FIGS. 6 a through 6 f illustrate alternative deployments for anultrasonic acoustic noise filter(s) according to the invention. In theseembodiments, note that the SAFE product is provided in accordance withthe invention as illustrated through FIG. 4, and the destroyer productis provided in accordance with the illustrations of FIG. 3. Referring toFIGS. 6 c and 6 f, in one arrangement, the SAFE noise filter (e.g., 410)is shown disposed in a flow stream defined between a meter and a noisesource. As described previously, the noise filter 410 is capable ofattenuating ultrasonic noise, particularly indirect noise, up to 45 dB.In these Figures, a blind tee is utilized in combination with the noisefilter 410, to deflect ultrasonic noise so as to generate indirectultrasonic noise. In particular, the blind tee eliminates the directacoustic line of sight relation between the noise source and the meter,thereby deflecting a portion of the direct noise (while also attenuatingup to 8 dB).

In yet another aspect of the invention, a fluid flow system arrangement,as shown in FIG. 6 e, is provided in which the meter and the noisesource are in serial relation within a fluid flow stream. In particular,the meter and noise source are disposed in fluid communication with eachother and in a substantially straight piping run between them. In otherwords, the meter and the noise source, absent some obstruction in thefluid flow stream, are positioned so as to be in direct acoustic line ofsight relation. In accordance with the invention, such an arrangementbetween the meter and a noise source is made possible through use of anultrasonic noise filter 410. As discussed previously, incorporation ofthe noise filter 410 in the fluid flow system of FIG. 6 e (without noisefilter 310) effectively attenuates the noise up to about 20 to 30 dB ofsubstantially direct noise without a significant direct noisecomponent). Again, as discussed previously, the deployment of the noisefilter 410 effectively attenuates much of the significant portion of theindirect noise generated by the noise source, and also throughreflection (e.g., by presenting non-porous or flow restrictive surfacesprovided primarily on the upstream webbing plate).

Preferably, a fluid flow system arrangement as shown in FIG. 6 e willalso include a second noise filter 310. Particularly, the second noisefilter 310 is used to eliminate the line of sight relation between themeter and the noise source. In this manner, as discussed previously, thenoise filter 310 effectively deflects direct ultrasonic noise, therebyattenuating ultrasonic noise by as much as 8 dB. More importantly, thenoise filter 310 deflects direct ultrasonic noise so as to convert thedirect noise to indirect noise, as it exits downstream of the noisefilter 310. This indirect noise can then be absorbed by the absorbentmaterials of the noise filter 410. In this manner, the combination ofthe noise filter 310 (primarily a deflector element) and the noisefilter 410 (primarily an absorbent element) attenuates the ultrasonicnoise up to about 40 dB to 50 dB.

FIGS. 7 a and 7 b reflect performance results using the noise filters ofthe present invented method demonstrating its improved performance.

It should be understood, however, that various arrangements anddeployments of acoustic noise filtering devices in accordance with theinvention may be made and will vary according to the particularenvironment and applications. However, in any such applications, variousaspects of the inventions will be applicable, as described above.

The foregoing description of the present invention has been presentedfor purposes of illustration description. It is to be noted that thedescription is not intended to limit invention to the system, apparatus,and method disclosed herein. Various aspects of the invention asdescribed above may be applicable to other types of fluid flow systemsand methods for filtering noise, or for attenuating ultrasonic noise. Itis be noted also that the invention is embodied in the method described,the system and apparatus utilized in the methods, and in the relatedcomponents and subsystems. For example, elements of the ultrasonicacoustic noise filter described above, for example the use andconfiguration of the absorbent material, or the use or configuration ofthe flow channels to eliminate the line of sight, may be implemented inother fluid flow applications or devices. These variations of theinvention will become apparent to one skilled in the acoustics, fluidmechanics, or other relevant art, provided with the present disclosure.Consequently, variations and modifications commensurate with the aboveteachings and the skill and knowledge of the relevant art are within thescope of the present invention. The embodiments described andillustrated herein are further intended to explain the best modes forpracticing the invention, and to enable others skilled in the art toutilize the invention and other embodiments and with variousmodifications required by the particular applications or uses of thepresent invention.

1. A fluid flow system comprising: a fluid flow conduit; a noise sourcedisposed in said fluid flow conduit such that ultrasonic noise generatedby said noise source propagates in said fluid flow conduit; and anultrasonic noise filter apparatus disposed in said fluid flow conduit,said noise filter apparatus including a first noise filter and a secondnoise filter; wherein said first noise filter includes an absorbentelement constructed to attenuate ultrasonic noise propagating from saidnoise source in the direction of said first and second noise filters;and wherein said second noise filter is disposed in said fluid flowconduit between said first noise filter and said noise source andincludes a deflector element positioned to deflect ultrasonic noisepropagating from said noise source before the noise source passes tosaid first noise filter.
 2. The fluid flow system of claim 1, whereinsaid deflector element is acoustically positioned in said fluid flowconduit so as to provide the sole direct line of sight acousticobstruction between said noise source and said first and second noisefilters.
 3. The fluid flow system of claim 2, wherein said second noisefilter includes a plurality of said deflector elements, said deflectorelement having a configuration defining a flow path with an entrance andan exit, and wherein said entrance and said exit are offset to eliminatedirect line of sight therebetween.
 4. The fluid flow system of claim 1,wherein said second noise filter includes a plurality of said deflectorelements, said deflector elements having a configuration defining a flowpath with an entrance and an exit, wherein said entrance and said exitare offset to eliminate direct line of sight therebetween and whereinsaid deflector elements are positioned such that, in a plurality ofdeflector elements, each deflector element rotated in one direction ispositioned adjacent a deflector element rotated in a counter direction.5. The fluid flow system of claim 1, further comprising: an ultrasonicdevice operable at ultrasonic frequencies, said ultrasonic device beingdisposed in said fluid flow conduit such that said first and secondnoise filters are positioned intermediate said ultrasonic device andsaid noise source.
 6. The fluid flow system of claim 5, wherein saidsecond noise filter is acoustically positioned in said fluid flowconduit so as to provide the sole direct line of sight obstructionbetween said noise source and said ultrasonic device.
 7. The fluid flowsystem of claim 5, wherein said noise source is a control valve and saidultrasonic device is an ultrasonic meter.
 8. The fluid flow system ofclaim 7, wherein said meter, said noise filter apparatus, and saidcontrol valve define a substantially straight flow stream thereacross.9. The fluid flow system of claim 1, wherein said deflector element isconfigured to convert directly propagating noise to indirectlypropagating noise.
 10. The fluid flow system of claim 1, wherein saidabsorbent element includes an absorbent material configured to convertultrasonic acoustic motion to vibration, thereby attenuating ultrasonicnoise.
 11. The fluid flow system of claim 10, wherein said fluid flowconduit defines a fluid flow stream and wherein said absorbent materialis disposed in generally parallel relation with said flow stream. 12.The fluid flow system of claim 11, wherein said absorbent materialincludes suspended, vibratable members of said absorbent materialpositioned into said flow stream.
 13. The fluid flow system of claim 10,wherein said absorbent material is a fibrous material.
 14. The fluidflow system of claim 10, wherein said absorbent element includes lateralsections formed by spirally wound layers of said absorbent material. 15.The fluid flow system of claim 14, wherein said fluid flow conduitdefines a fluid flow stream and wherein said lateral sections overlap toform protrusions into said flow stream.
 16. The fluid flow system ofclaim 14, wherein said lateral sections include pairs of said spirallywound layers of absorbent material that are adjacent one another anddisposed in opposite spiral wound relation.
 17. The fluid flow system ofclaim 10, wherein said absorbent material is polyester.
 18. The fluidflow system of claim 1, wherein said first noise filter includes aplurality of channels each defining a flow path, and an absorbent wallsurface positioned in generally parallel relation with said flow pathand whereon absorbent material of said absorbent element is disposed.19. The fluid flow system of claim 18, wherein said first noise filterincludes a longitudinal centerline and a plurality of outside channelspositioned radially equidistant from said longitudinal centerline. 20.The fluid flow system of claim 19, wherein said first noise filterincludes an inside channel positioned about said longitudinalcenterline, said inside channel having an inside surface whereon saidabsorbent material is disposed.
 21. The fluid flow system of claim 19,wherein said outside channels include an absorbent wall surface whereonsaid absorbent material is disposed and an oppositely facing exposedsurface free of said absorbent material, said absorbent and exposed wallsurfaces defining a maximum gap therebetween.
 22. The fluid flow systemof claim 21, wherein said outside channel includes an entrance, saidentrance including a lip positioned acoustically upstream of andadjacent said absorbent wall surface, such that a maximum gap betweensaid lip and said exposed surface is less than said maximum gap betweensaid absorbent wall surface and said exposed wall surface, and whereinsaid lip is adapted to generate turbulent flow immediately downstreamthereof.